A brake force booster of the afore-described type and the way of fixing the movable wall thereof to the control valve housing is known to those skilled in the art. The diaphragm plate of such brake booster, in the radially inward area thereof, comprises a circumferential curvature seated on a rectangular support surface formed on a control valve housing such that in case of a pressure load on the movable partition wall, a rolling movement of the diaphragm plate may take place. The support surface of the diaphragm plate is followed by a groove of rectangular cross-section accommodating a bead correspondingly shaped in the radial-inward area of the rolling diaphragm.
However, in prior known brake force boosters of this type, in predetermined operating conditions, the rolling diaphragm is likely to be detached, thereby substantially affecting the operating safety of the system. This danger occurs especially as a result of stagnation pressure in the brake system through actuation thereof without vacuum and with closed check valve outlets, respectively, since the view of the pressure prevailing in the brake force booster housing force components are formed which act in the radial direction, tending to withdraw the annular bead of the rolling diaphragm from the circumferential groove of the control valve housing and to displace the diaphragm plate in a direction opposite the actuating force, thereby forcing the annular bead out of the groove. This will result in the failure of the brake system the boosting force of which no longer can be built up.
Equally disadvantageous are the material tensions or stresses in the control valve housing particularly high in view of the rectangular configuration of the support face of the diaphragm plate and of the groove accommodating the rolling diaphragm, which tensions, in predetermined circumstances, are likely to destroy the control valve housing.